Paper article coated with a slip coating of a partial ester of a fatty acid



United States Patent 3,455,726 PAPER ARTICLE COATED WITH A SLIP COATING OF A PARTIAL ESTER OF A FATTY ACID Charles T. Mitchell, Jr., North Reading, and William F. Scheufele, South Natick, Mass., assignors to W. R. Grace & Co., Cambridge, Mass., a corporation of Connecticut No Drawing. Filed Feb. 10, 1966, Ser. No. 526,409 Int. Cl. B44d 1/16 US. Cl. 117-76 4 Claims ABSTRACT OF THE DISCLOSURE A substrate such as paper is coated with a moistureresistant film (e.g. a vinylidene chloride polymer) over which is deposited a partial ester of a fatty acid and hexitol anhydride (e.g. sorbitan monostearate) to increase slipperiness of the film surface.

This invention relates to articles coated with a slip agent and which is particularly useful in the preparation of spiral-wound tubular paper cans.

Spiral-wound tubular paper cans have been adapted for packaging a number of materials. The spiral-wound tubes are made on a spiral winder. In brief, this machine consists of a stationary round steel mandrel over one end of which is looped an endless belt, while the other end has a traveling saw. The raw paper stock, i.e., flexible paperboard or paper of the type used in manufacturing paper cans, is slit into narrow rolls which are fed into the winder from either side.

Each web of paper passes over a glue roll and from there around the mandrel and under the endless belt at an angle of 45 to 60. The pressure of the moving belt causes the formed tube to rotate on the mandrel, thus drawing in more material and causing the formed tube to move forward in a helical motion along the mandrel. The continuous spiral tube may be cut to size on the winder or as a separate operation. The cut tubes are then placed in a press and the ends of the tubes are flared to receive the can end.

Paper cans are normally provided with a foil lining or a film or coating of a material which bars moisture penetration. Representative of the moisture barriers are coatings formed from vinylidene chloride polymers. These coatings, and moisture barrier materials in general, suffer from a lack of slip, i.e., the film-to-metal coetficient of friction is high. This is a serious handicap in the formation of paper cans because it results in jamming of automatic machinery and dilficulty in removing the tubes from the mandrel.

In an actual operation, for example, the webs of paper are provided with a vinylidene chloride polymer coating. The coated webs are fed into the belt loop and wrapped around the mandrel. This action produces a great deal of frictional heat and galling, i.e., wearing away by friction, of the coating. The mandrel, if uncooled, will heat up to a temperature of 200 F. and the coating will adhere to the mandrel causing a shutdown and requiring cleaning and rethreading. A water-cooled mandrel offers a slight improvement in that the temperature can be kept below 150 F., but galling still occurs. The desired winding speed of 300 to 1000 feet per minute requires a slip coat of some type even on foil lined cans.

Various agents of different types have been proposed for use as slip agents, but most of the materials of the prior art have had one or more defects which detract from their usefulness on a practical commercial scale. Some do not impart the desired slip; others are effective only in relatively large amounts so that use thereof increases the ICC manufacturing cost of the cams too greatly; still others fail to give good slip at the higher temperatures to which the tube is subjected when it is exposed to heat developed by friction on the mandrel; or they do not have the hardness necessary to protect the barrier material from galling.

Specifically, one of the methods used to reduce the friction between a steel mandrel and a vinylidene chloride polymer coated paper web was to apply a lubricant to the coating as the coated web was wound on the mandrel. Various water solutions and oils were applied, but these materials built up on the mandrel and resulted in streaks, galling, and oversized can bodies. Another method was to top coat the vinylidene chloride polymer coating with a slippery material such as wax, oil, and soap. Many of the oil additives, floor waxes buffed and unpolished, metal stearate soaps, and silicone oils were found to increase the friction as measured by the angle indicative of the coeflicient of friction.

The angle indicative of the coefficient of friction was measured in the following manner. A steel block weight was used which was 1.9 inches in height, 2 inches in width, and 4 inches in length, having at each end of the bottom a step 1 inch in length, 2 inches in width, and 0.25 inch in height, which was the surface in contact with the slip coated sheet being tested. The weight of the block was 4 pounds or 1 pound per square inch in the horizontal position. The slip composition was coated on kraft paper or similar type of paper and dried. The coated paper was attached to a smooth wooden board with Scotch tape with the uncoated side of the paper adjacent to the wooden board. The weight was placed on the coated surface of the paper, and the board was slowly tilted until slippage occurred. This angle was recorded as an indication of the static coefiicient of friction.

In measuring the angle indicative of the kinetic coetficient of friction, the board was raised to a predetermined angle and the weight was then placed on the coated surface of the paper, and the weight was observed to see if slip occurred. The angle of the board was then changed in the proper direction, and the weight again was placed on the coated surface. The angle at which the weight slipped was reported as an indication of the kinetic coeflicient of friction.

It is a principal object of the present invention to provide an article useful in the preparation of spiral-wound cans and which overcomes the defects of the prior art.

The novel article of the present invention comprises a solution of partial esters of a fatty acid and hexitol anhydride which is applied to a substrate. The solutions are water solutions or solutions in organic solvents. Organic solvents known to the art are employed in the present invention; for example, toluene, isopropanol, xylol, methanol, and perchloroethylene. In a preferred embodiment, the partial ester of a fatty acid and hexitol anhydride is employed in isopropanol solution. As examples of such partial esters of fatty acids and hexitol anhydrides, mention may be made of the Spans and Arlacels (trademarks of the Atlas Powder Company, Wilmington, Del.).

The slip agents are employed as 0.5 to 25 percent by Weight solutions. In a preferred embodiment, a 2 percent solution is employed.

In an alternative embodiment, the slip agent also includes a polyoxyethylene derivative of fatty acid partial esters of hexitol anhydrides. The partial ester of fatty acids and hexitol anhydrides and the polyoxyethylene derivatives thereof are preferably employed in a 1 to 1 ratio on a weight basis.

The method of depositing a coating of the slip agent on the substrate is not critical. Any type of coating mechanism or device which is capable of depositing the uniform amount in the desired thickness of the substrate may be employed. Special types which may be used include air knife coater, horizontal and vertical size presses, trailing blade, transfer roll, reverse roll, roller coater, gravure bead coat, metering bar, spray coater, and curtain coater. Deposition may be carried out in one or a number of applications, and the amount deposited is such as to provide a. dry weight coating ranging between about 0.1 to 1.0 pound per 3000 square feet of substrate. Dry weight coatings ranging from about 0.2 to 0.5 pound per 3000 square feet are particularly satisfactory. The slip coated substrate is then dried either in air or a suitable drying apparatus. Air drying can be accomplished in less than minutes while oven drying can be effected within 10 to 30 seconds at an oven temperature of 120 to 130 C. The dried slip coating is odorless, clear, and very glossy.

The slip compositions were tested in the following manner.

An aqueous vinylidene chloride copolymer emulsion (Daran 210 trademark of W. R. Grace & Co., Cambridge, Mass.) was coated on one side of a large piece of flexible paperboard of the type used in forming spiralwound paper containers. The paperboard was about 17 mils thick.

The following are typical properties of the vinylidene chloride copolymer emulsion.

Total solids About 60%. Color Cream white. Freezing point 36 F.

Particle size .13 avg. (micron). Specific gravity 1.320 i0.0l5.

The polymer emulsion (Daran 210) was applied to the paperboard with a roller and then levelled with a No. 6 Mayer rod. The coated paperboard was initially dried by passing it under infra red lights and then through an oven maintained at 250 F. The dried coated paperboard was then passed again under the infra red lights to fuse the dried vinylidene chloride polymer coating. The web speed was 350 feet per minute. The weight of the dried coating was approximately 8 pounds per ream (3000 sq. ft.).

A second coating of the vinylidene chloride polymer emulsion (Daran 210) was applied to the dried coating in the same manner except that a No. 4 Mayer rod was used and that drying temperatures of the first and second zones of the oven were maintained at 300 F. The weight of the dried coating was approximately 2.8 pounds per ream (3000 sq. ft.). A third coating of the vinylidene chloride polymer emulsion was applied in the same manner as the second coating, and the coating weight was approximately 3.6 pounds per ream (3000 sq. ft.). The total weight of the coating was approximately 14.4 pounds per ream (3000 sq. ft), and the total thickness of the paperboard and the coating was about 18 mils. The vinylidene chloride polymer coating was colorless, clear, smooth, continuous, and glossy.

The slip composition under test was applied to the above-described coated paper with a roller and then levelled with a Mayer rod. The slip coated paperboard was initially dried by passing it under infra red lamps and then through an oven maintained at 300 F.

The following nonlimiting examples illustrate the novel slip compositions of the present invention.

Example 1 A 2 percent by weight solution of sorbitan monostearate in isopropanol was prepared and coated on paperboard in the manner described above. The slip characteristics of 4 Example 2 A 1 percent solution of sorbitan monostearate in isopropanol was prepared and coated on flexible paperboard in the manner described above. The slip characteristics of the coated paperboard are shown below.

Mayer rod Static angle Kinetic angle Example 3 A 4 percent solution of a 1 to 1 mixture of sorbitan monostearate and polyoxyethylene sorbitan monostearate in isopropanol was prepared. The composition was then coated on paperboard as described above and the slip characteristics were then determined.

Mayer rod Static angle Kinetic angle Example 4 The solution of Example 3 was diluted with isopropanol to provide a 2 percent solution, the slip characteristics were then determined on coated paperboard as in the A 20 percent solution of a 1 to 1 mixture of sorbitan monostrate and polyoxyethylene sorbitan monostearate in water was prepared. The slip composition was applied to paperboard and the slip characteristics were determined.

Mayer rod Static angle Kinetic angle Example 6 The solution prepared in Example 4 was diluted with water to provide a 2 percent solution and then coated on paperboard. The slip characteristics were then determined.

Mayer rod Static angle 1 Kinetic angle Examples 7-13 A series of partial esters of fatty acid and hexitol anhydride were tested for slip characteristics according to to the procedure of Example 1. Solutions '(2 percent in toluene) were coated on flexible paper-board with a No. 4 Mayer rod. The slip characteristics of the coated paperboard are shown below.

Ex. No. Slip agent Static angle Kinetic angle 7 Sorbitan monolaurate 10 7. 5 Sorbitan monopalmitate- 9 7. 5

Sorbitan monostearate. 10 8 Sorbitan tristearate 9 7. 5

Sorbitan monooleate- 8 7 Sorbitan trioleate 9 7 13 Sorbitan sesquioleate 9 7 For comparative purposes, toluene alone and water alone as controls were applied to coated paper in the same manner as the slip agents above, and measured for slip characteristics.

TOLUENE CONTROL Mayer rod No. Static angle Kinetic angle WATER CONTROL Mayer rod N 0. Static angle Kinetic angle Althouh the slip compositions have been described primarily in terms of use with paper coated with vinylidene chloride polymer, the compositions are also used satisfactorily on polyethylene and polypropylene films to provide the desired degree of slip.

The compositions described in the present invention have been used on coated paper which is formed into spiral-Wound cans on a mandrel at 300 feet per minute at 190 F. without jamming, galling, or other indications of excessive friction.

What is claimed is:

1. An article comprising a paper substrate, a moisture resistant film of a polymer selected from the group consisting of vinylidene chloride polymer, polyethylene and polypropylene superimposed on said substrate, and a slip coating on said film, said slip coating consisting essentially of a partial ester of a fatty acid and hexitol anhydride, the amount of said slip coating on said film ranging between about 0.1 to 1 pound per 3000 square feet of said substrate.

2. An article as defined in claim 1 wherein said mois ture-resistant film is a vinylidene chloride copolymer film.

3. An article as defined in claim 1 wherein said slip coating additionally contains a polyoxyethylene derivative of a partial ester of a fatty acid and hexitol anhydride.

4. An article as defined in claim 1 wherein said partial ester of a fatty acid and hexitol anhydride is sorbitan monostearate.

References Cited UNITED STATES PATENTS 2,565,403 8/1951 Sproule et a]. 2,628,176 2/ 1953 Simon et a1. 3,132,041 5/1964 Pihl. 3,200,005 8/ 1965 Bauer.

WILLIAM D. MARTIN, Primary Examiner R. HUSACK, Assistant Examiner US. Cl. X.R. ll790 

